电气外文翻译

翻译部分中文译文中压补偿电网间歇性接地故障检测摘要-从波兰中压电力配网获得的经验表明应用于间歇性接地故障的故障点定位判据是不可靠的，这主要是因为不稳定性，还有低功率水平的测量信号常常衰减到了保护动作值以下。本文提出来一种新的基于小波分析的自适应算法，这种算法能够动态检测间歇性接地故障中的测量信号。本算法利用EMTP程序包产生的信号进行分析验证。1、前言一般来说，波兰的中压配网采用中性点经消弧线圈接地的方式。经查证，农村地区线路大部分是架空线路。这种网络的特征是90%的线路故障是接地故障。这主要因为故障点较高的过渡电阻和一些天气因素如闪电，狂风，高温和低温等的影响，这些因素都将导致传输线路的老化，破裂，从而导致接地故障的发生。由于上述接地故障特征的干扰，使得检测定位故障点也比较困难。主要讨论如下故障类型：高阻抗%接地故障；进线侧线路短路过程中的闪落；周期的和非周期发生的故障；一个实际的故障可以表现出上述所有特征。本文所做的分析仅限于间歇性接地故障过程中的自动保护单元。为了评估保护的运行性能，在故障过程中测量信号的特征和等级均是被标定了的。电网发生间歇性接地时最重要的信号指示是零序电压分量，该值可以通过计算瞬时相电压值求得。故障定位的判据如下：零序电流分量，I;0零序电压分量U0，零序电流分量10计算所得零序功率；零序电流和零序电压分量的相位角：零序导纳y，或者它的实部气，和虚部气；然而，上述判据值在间歇性接地故障发生时就不一定准确了。2、网络模型为了模拟和研究间歇型接地故障现象，本文给出了一种典型的中压对称网络。网络模型如下图所示：

Mm.,Fig.lMediumvoltage-networkschenie故障采用EMTP/ATP程序仿真，电网的仿真参数设置如下表所示:Mm.,15Kv模拟电网参数电网电容电流I0101.3A故障线路电容电流I0110.6A补偿度+15%过渡电阻RF2在上述模型中，假定故障线路接地电容电流为10.6A，负载功率为150kW。本文分别分析了以下故障类型：A、永久性故障；B、持续时间和中断时间均为10ms的间歇性接地故障；C、持续时间为10ms，中断时间为100ms的间歇性接地故障；D、持续时间为50ms，中断时间为50ms的间歇性接地故障；所有的故障类型均在线路1的初始端进行模拟，即靠近母线侧。记录如下数值:零序电压分量U0，故障线路零序电流分量101和非故障线路零序电流分量102。3、实验结一导纳判据在第一节强调的保护判据里面，对于比较复杂的故障如间歇性接地故障，最有效的判据是零序导纳K，或者它的实部G，和虚部B为了实现导纳型故障保护，使用了幅值比较器（见图2中CA1,CA2）。简单模型中，输入信号按照如下规则进行比较：TOC\o"1-5"\h\z*=匕匕■；（1）52=kU0；（2）七=kU0；（3）其中，k，k，k为测量过程中处理输入信号的对应系数。123Fig.2.Admittance-typeearthfaultprotecticn-Fig.2.Admittance-typeearthfaultprotecticn-equivalentschemeCAI^CA2接地故障保护反应于零序导纳模块信号土和土比较单元。比较发生在幅值比较器CA1，当满足下式：§<52；（4）第i条线路保护动作。这也意味着第i条线路的保护动作区域由如下导纳向量y=n>、；（5）01Uk02所决定。图3表示了这种保护的启动响应，它仅仅是一个普通的同样包含复导纳平面所有部分的谱图。保护动作辅助部分是适当水平的零序电压分量。本方案中，启动单元是比较器CA2，CA2中信号53和启动信号53依据下式比较：S3=kU0>54；（6）其中54是按照根据接地故障时和正常电网的不同设定的初始值。

^Jpeuiriiigcharacren^ricFig.3.Srart-uyresponseofrheadmitrance-T^peearth-faulprotection图4中表示了线路1发生永久性故障时的故障线路零序电流分量101和非故障线路I，零序电压分量U，故障线路零序导纳K，非故障线路零序导纳K。0200102Fig.4Conriiivousearthfault(Atype)-mline1测得的故障线路零序导纳将高于非故障线路。依据判据4分辨故障线路不会造成判断问题。类似的，间歇性接地故障截止频率高，相应的幅值如图5所示。由于故障发生时暂态的延迟作用，零序电压仍为发生永久故障时电压值，并且测得故障线路的导纳将持续明显高于非故障线路。(VJyCVIM(WM-m.rm》#ESWSHIN.Rys.5.Lnt^ruurteutearthfaul(B-type)mlineLHine(niF电6BLremuttentearrhfault(C-type)inline1Fig.7LttemiitTenrearrlifault（D-rype）inlineL短路线路中断时间比较长时（如C型和D型故障）描述比较困难。该类故障运行曲线如图6和图7所示。故障持续期间，零序电压分量（对应于保护启动信号七）保持较大值，再考虑故障发生后立即出现的比较小的衰减的暂态电压分量，这就意味着检测故障不难。然而，如何描述故障线路却有点问题。这是因为暂态过程中，故障点周期性的电弧引燃，故障线路的导纳相应于非故障线路会周期性的下降。C型和D型故障均是这种情况，此时，相关的导纳判据也是不正确的。利用小波展开将会是一个好的选择，特别是对于多分辨率的信号分解方面。4、多分辨率小波分析小波分析作为一种主要工具应用在测量信号的多分辨率分解方面，这主要通过多级的小波补充滤波（高通和低通的定比函数）实现的。程序实现分解算法为Mallat法则。创造多分辨率信号表示的迭代处理过程可以用图8所示的小波信号分解树演示。任何一步迭代过程，所分析均是被过滤过的。迭代的阶次也不是无限制的，如图8中，n为假定的阶次。每一个迭代结果包含两部分：称作Q的高频分量，它在连续迭代步骤中不再过滤；用于分析初始信号S的低频分量A，ii称作应用近似值。因此，信号分解过程有一种多级迭代过程实现低通滤波，并且连续近似和连续分解过程相反。选择用于信号分析的母小波如图5,6,7所示，当用于分析信号频谱时，光滑的小波分解信号较好，因为它们有较好的频域局部性，尖形的小波有较好的时域局部性。综观大多小波类型，作者得出，Haar小波的特性能够更好的满足本方案应用要求，因为它的保护中实时计算速度快，区分度好。基本的Harr小波按照如下定义：…11(0jfJ2)1(7)w(t)={-1(；<t<1)20(其它)(7)小波元素系列如下：中(t)=2-m/2中(2-mt-n)m,n=…，-2,-1,0,1,2,…(8)函数wmn在所提议应用中的优点主要是通过任意函数中断的精确定位，可以获得时域的无限精确定位（尤其对于迭代步骤，见图5和图6）,函数的分解通过小波列定义。Haar小波缩放函数满足如下关系：11(0<t<1)（9）'(t)=〔0(其它)（9）众所周知，多级分解是以高速计算性能为代价的。在一个简单的Haar小波应用实例中，每一步分解均限于计算平均值（低通）或者微分值（高通）。平均值是一种粗略的表示（近似），而微分值是一种精确的表示。7■-T，｝…||I二I[A11Fig.®Signalwaveletdecompositiontrre（^T））5、间歇性接地故障中测量信号的多级分解和故障线路描述为了更好的描述接地故障线路，本文使用第四节所讨论的测量信号分解的迭代方法。本文分析了故障线路零序电流101,非故障线路零序电流102。图9~14展示了B,C,D型间歇，性故障时获得的信号和六级分解的情况。图示结果通过基本Haar小波变换获得，采样频率为10kHz。图中，信号的频率特征不明显，但幅值和时间位置却很明显，在的，d1,d2,d3级中即时相位变换现象尤其明显。在更高级的分解中，如d4,d5,d6中，相位变换现象就不那么明显了（非故障线路）或者成为主要成分了（故障线路）。这种现象可以作为区别故障线路和非故障线路的依据。信号中断时的尖形突出将会导致信号平均值远低于信号的峰值。

在d4,d5,d6级中包含高频成分，平均值绝对值、）的执行比例和在宽度N的数据窗中计算得的第K个值满足如下关系：i=NEabs[i（k-n）]；n（10）间歇性接地故障中短路线路的描述通过比较C和起始值二,实现，C代表瞬时电流绝对值与平均值的比值。C=abs(i(C=abs(i(k))>C；（11）一L(k)''.ofcumenlB-type-intermitXZ7T二二二XZ7T二二二Time,ms二A；0.25-r-a6o「八一■025十-

0R.ys.11.Five-leAreldecompositionofcuneiitsignal.damagedline,

C-typemteritiittetttfault1-rTOC\o"1-5"\h\z0,5丁二「了—；d40^fiR^^^j^******^^******^^**^-0,54\0.51—二；二[一二二—n—!d5o-□5【!1了—-.：[::=d6o!a^aa^amv^'/J^WJ叫叫v叫1q%A(v^1【!0251a6o^v/Y/x/^^^x/Y/xzNz^x^zx/x/vzx^^x/y/x^-0J5X1\o"CurrentDocument"0Time,ms4"Fig.12Five-LeveldecompositionofcurrentsignalZ02；undamagedline.C-typeintermittentfault-0.25+T0Time,ms。钊Rys.13.Five-leveldecctnposirionofcurrentsigiiaLJq2；damagedlineD-1ypeinteTtnitteutfault证实当保护满足式（11）条件时，断路器会断开，零序电压分量（OS1=1）接地故障仍然存在，任何切断保护导纳部分（OS2=0）脉冲（OS）均不发出

证实Rys.14.Five-leveldecompositionofcurrent2d‘：undamagedline.Fig„l5.DiscrimuLationalgoritliwforlinewithmteinjittenifeiilt（csroiLudCPAC}图16中，表示了一种自适应接地故障保护的方案框图，它是对传统导纳保护（见图2）的延伸。基本的补充模块有：测量信号多级分解模块WD模块，实现线路描述算法的PAC比较器（峰值-均值比较器）（见图15）。Rys.1ft.Adaptiveearthfaultprctectiou—blockscheme鉴于传统保护判据的不可靠性，上述保护的逻辑结构中，WD模块和PAC模块增强了保护运行过程中故障消除的能力和可靠性。6、结语本文间歇性接地故障实验中测得信号U0和10表明，传统保护设备在确定这类故障和鉴别故障线路方面存在一些问题。如果故障间中断时间超过10ms，检测困难也会增加。因为这种中断也会在不平衡配网中出现，一些接地故障时保护不动作情况自然也会出现。因此，基于消除此类问题的新的保护判据也正在研究当中。经过分析间歇性接地故障实验，我们很容易得出，多级小波分解能够甄别被保护线路的信号特征。本文所有例子表明，故障线路和非故障线路原始信号在初级分解（d1，d2，d3）中干扰比较明显。而在高级分解之中，故障和非故障线路的谱图明显不同，这也促进了分辨故障线路，排除故障。7、参考文献S.Mallat,"ATheoryformultiresolutionsignaldecomposition:thewaveletrepresentation",IEEETrans.OnPatternAnalysisandMachineIntelligence,Vol11,No7,1989,pp.674-693.Shyh-JierHuang,Cheng-TaoHsieh,Ching-LienHuang,"Applicationofwaveletstoclassifypowersystemdisturbances"ElectricalPowerandEnergySystem,47,1998,pp.87-93.O.Chilard.,L.Morel.,D.Renon.,"Compensatedgroundedmediumvoltagenetworkprotectionagainstresistivephasetogroundfaults",CIRED,Nice1999AburA.,MagnanoF.H.,"Useoftimedelaysbetweenmodalcomponentsinwaveletbasedfaultlocation",ElectricalPowerandEnergySystem,22,2000,pp.397-403LobosT.,RezmerJ.,"Wavelettransformsforreal-timeestimationoftransmissionlineimpedanceundertransientconditions",ElectricalEngineering,84,2002,pp.63-70.D.Chanda,N.K.Kishora,A.K.Sinha,"Awaveletmultiresolutionanalysisforlocationoffaultsontransmissionlines",ElectricalPowerandEnergySystem,25,2003,pp.59-69.8、作者简介JozefLoren，生于1949年，波兰的小镇Jarocin，获得波兹南科技大学电气工程专业的硕士和博士学位。目前，职称为副教授，担任电气电力工程学会主任。从事电力系统继电保护领域工作，主要研究电网保护判据、无功补偿、中压配网中性点运行、接地保护、电流冲击保护等方面。KazimierzMusierowicz，生于1943年，于1969年毕业于弗罗茨瓦夫科技大学电气工程专业，获得波兹南科技大学硕士学位，现为该校讲师和研究员。从事电力系统继电保护和数字信号处理领域的研究工作。AndrzejKwapisz，生于1971年，波兰的小镇Szczecinek，获得波兹南科技大学硕士学位。目前为该校研究员。主要从事电力系统数字技术，计算机辅助电力系统分析，暂态和稳态电力系统仿真，继电器开发标准等领域研究工作。英文原文DetectionoftheIntermittentEarthFaults

inCompensatedMVNetworkJozefLorenc*/,KazimierzMusierowicz*/,AndrzejKwapisz*/Abstract-TheexperienceacquiredfromthePolishmediumvoltagepowerdistributionnetworksshowstheunreliabilityofthelocalizationcriterionsappliedtotheintermittentearthfaults.Itresultsfromthelackofstabilityandlowpowerlevelofthemeasuringsignalsfallingoftendownbelowtheprotection’sstart-uplevel.Inthepaper,anewadaptivealgorithmbasedonthewaveletanalysisenablingdetectionofspecificdynamicsofthemeasuringsignalduringintermittentearthfaultsispresented.ThealgorithmwasanalyzedutilizingthesignalsgeneratedintheEMTPprogrampackage.INTRODUCTIONIngeneral,theMVdistributionnetworksinPolandoperatewiththeneutralpointgroundedthroughthecoiltocompensatethecapacitiveshortcircuitcurrenttotheearth.Itrefersmainlytotheruralareanetworkswherethelinesaretheoverheadones.Suchnetworksarecharacterizedbylargenumberoftheearthfaultsexceeding90%ofallrecordedfaults.Duetotherelativelyhighcrossresistanceatthedefecfslocation(RF)aswellastotheeffectsoftheweatherphenomenasuchasdischarges,gustsofwind,highandlowtemperaturesresultingintheruptureofthelineconductorscontinuity,theearthfaultsoccur.Characteristicsofthesefaultsmakesimpossiblethedetectionandlocalizationofsuchdisturbance[3].Thefollowingfaulttypescanbeencounteredtothediscussedfaultsgroup:-resistancefaultsofhighcrossresistance,R,-breakinthelivewireshortcircuitonthereceiverside,-faultsbeingbrokencyclicallyandnon-cyclically.Anactualfaultcanshoweitheroneorallofthelistedfeatures.Inthepaper,theanalysisislimitedtotheautomaticprotectiveunitsoperationduringintermittentfaults.Toassesstheprotection’soperability,thelevelsandfeaturesofmeasuringsignalswhichcanoccurduringthefaultaretobeidentified.Themostimportantsignalindicatingoccurrenceoftheintermittentearthfaultinthenetworkisazero-voltagecomponentthevaluesofwhichisoftenfoundbyaddingtheinstantvaluesofphasevoltages.Thecriterionvalueofthefaultlocalizationcanbe:-zerocurrentcomponent,I0-powerofthezerocurrentcomponent,I,andzerovoltagecomponent,U,-phaseshiftanglebetweenthezerocurrentandvoltagecomponents,-zeroadmittancecomponent,Y,oritscomponents:activeGorreactive.BHowever,thecriterionvaluesaslistedaboveareoftenunreliablewhenthe

intermittentearthfaultoccurs.MODELOFNETWORKFormodelingandstudiesoftheearthfaultphenomenaaccompanyingtheintermittentearthfaults,atypicalmediumvoltagebalancednetworkhasbeenchosen.TheschemeofmodelednetworkisshowninFig.1.mW,Fig.lMediumvoltage-networkschememW,ThefaultsweremodeledandsimulatedusingtheEMTP/ATPprogrampackage.ChosenparametersofnetworkassumedforsimulationpurposesareshowninTable1.TABLE1MODELLED15KVNETWORKPARAMETERSNetworkcapacitycurrentI0101,3AFaultlinecapacitycurrentI0110,6ADecompensationlevel+15%CrossresistanceRF2WInthemodeltheassumptionwasmadethatthefaultsoccurinalinewithto-ground-capacitivecurrentof10.6Aandamoderatedpowerloadof150kW.Thefollowingfaulttypeshavebeenconsidered:-A-type-continuousfault,-B-ype-intermittentfaultoftsc=10msdurationtime,tp=10mspausetime,-C-type-intermittentfaultoftsc=10msdurationtime,tp=100mspausetime,-D-type-intermittentfaultoftsc=50msdurationtime,tp=50mspausetime.Allfaultshavebeenmodelledatthebeginningoftheline1,adjacenttothebusbars.Thefollowingmagnitudeshavebeenregistered:networkvoltagezerocomponent,U,aswellasthezerocomponentcurrentofthedamagedline,I,andthatoftheundamagedline,I.RESULTSOFEXPERIMENTS-ADMITTANCECRITERIONAmongthecriterionvaluesforprotectionsasspecifiedinsection1,forthe‘difficult’faultcasessuchasintermittentearthones,themosteffectiveiseithertheadmittanceY0oroneofitscomponents:conductanceGorsusceptanceB.Toimplementtheadmittance-typeearthfaultprotections,theamplitudecomparators(CA1,CA2inFig2)areused.Inthesimplestcase,theinputsignalscreatedaccordingtothefollowingrulesarebeingcompared:TOC\o"1-5"\h\z*=々。-；(1)七=kU0；(2)§=kUo；(3)Thek,kandkcoefficientsdeterminetheproportionalityoftheinputsignalprocessingintheprocessinginthemeasuringpaths.Fig.2.Admittance-typeearthfiultprotection-equivalentschemeTheearthfaultprotectionrespondingtothezeroadmittancemodulecomparestheS1andS2signals.ThecomparisontakesplacewithintheamplitudecomparatorCAl.Theprotectioninthei-thlineactswhenTOC\o"1-5"\h\z§<S2;(4)Itmeansthattheoperationareaofprotectionlocatedinthei-thlineisdeterminedbytheendsofadmittancevectorsofvaluesmeetingthecondition:Y=匕>、;(5)01Uk02InFig.3,thestart-upresponseofsuchaprotectionisshown.Itisaplain-admittancecurveincludingequallyallquartersofthecomplexadmittanceplane.Supplementaryclauseoftheprotectionoperationisaproperlevelofvoltagezerocomponent.Insuchasolution,thestart-upunitistheamplitudecomparatorCA2inwhichtheS3signalleveliscomparedtothatoftheS4start-upsignallevel,accordingthetheclause:S3=kU0>S4；(6)wheretheS4isthepresetstart-upvalueduetowhichtheearthfaultcanbedifferentiatedfromthenormalnetworkoperation.F〔_g-3一Start-upresponseoftheadmitrance-r^peearth-faulprotectionInFig.4,thecurrentzerocomponentsinthedamagedline,I,andintheundamagedline,I,voltagezerocomponentUaswellaszero-admittancesinthedamagedline,Y,andundamagedlineY,duringcontinuousfault(A-type)inline1arepresented.Tini-e(nit)Fig.4Tini-e(nit)Fig.4Conriuvouseaithfault(A-type}inline1Thezeroadmittancemeasuredinthedamagedlineissome-foldhigherthanthatintheundamagedline.Discriminationofdamagedlineaccordingtocriterion(4)shouldnotposetheproblems.Similarcaseisforanintermittentfaultofrelativelyhighinterruptionfrequency(B-type),thecorrespondingrunsofnalysedmagnitudesareshowninFig.5.Afterdecayofthetransientstateresultingfromthefaultoccurrence,thezerovoltageremainsattheleveladjacenttohevoltageduringthecontinuousfault,andtheadmittancemeasuredinthedamagedlineisallthetimeevidentlyhigherthantheadmittancemeasuredintheundamagedline.rv.)M--1s■普■■=》liine(ms}Rys5Interiiutteutearthfaul(B-type)inline11.-.-=Vrv.)M--1s■普■■=》liine(ms}Rys5Interiiutteutearthfaul(B-type)inline11.-.-=V重密M号，EefflJ=mp<3=O>Tini-eJwouli-InnFig.6IcLTermirt<ntearrhfauh(C-type)inline1Adiscriminationoftheshort-circuitedlineincasewhenthepausebetweensuccessivefaultsisrelativelylong(longtimetp-CandDtypes)canbemoredifficult.Therunsrelatedtosuchfaultsareshowninfigures6and7.Duringentiredurationoffault,thevoltagezerocomponent(towhichthestart-upsignalS3isproportional)remainsatthehighlevel;itmeansthatthefaultdetectionshouldnotbedifficultduetotherelativelylowattenuationofthevoltagetransientsafterinstantaneousdisappearingofthefault.However,theproblemscouldarisewithdamagedlinediscrimination.Duetothefeaturesofthetransientprocessinthenetworkresultingfromthecyclicarcignitionsinthefaultlocation,thedamagedlineadmittancefallscyclicallydowntotheundamagedlineadmittancelevel.ItreferstoboththeC-typeandD-typefaults.Insuchacase,animproperoperationoftheadmittancecriterion-relatedprotectioncanbeexpected.Betteropportunitiesopenwhenusingthewaveletexpansions[2],[4],[5],especiallythemulti-resolutiondecomposition[6]ofthemeasuringsignals(WD).MULTI-RESOLUTIONWAVELETANALYSISAmaintoolofthewaveletanalysisintheproposedapplicationisthemulti-resolutiondecompositionofmeasuringsignalsrealizedbythemultistagesetofthewaveletcomplementaryfilters(high-passwaveletsandlow-passscalingfunctions).ThecalculatingprocedureleadingtothedecompositioniscalledtheMallatalgorithm[1].Theiterationprocessofcreatingthemulti-resolutionsignalrepresentationcanbepresentedintheformofthewaveletsignaldecompositiontreeasshowninFig.8.Atanyiterativestep,theanalysedsignalisfiltered.Thenumberofiterativestepsisunlimited;inFig.8,nstepshavebeenassumed.Eachiterationresultsinboth:thehigh-frequencycomponentcalledadetail(Di)whichisnomorefilteredduringsuccessiveiterativesteps,andthelow-frequencycomponent(Ai)ofanalysedoriginalsignalS,calledanapproximation.Thus,thesignaldecompositionprocesshasaformofthemultileveliterativeprocesscarriedoutonthelow-passfiltrationchannel,andthesuccessiveapproximationsaresubjecttothesuccessivedecomposition.Whenchoosingthemotherwaveletforanalysisofmeasuringsignalsshowninfigures5,6and7,theknownrulehasbeentakenintoaccountthe‘smooth-shape’wavelets(theMorlet'swavelet,forexample)areofbetterresolutionwhenanalysingthesignalfrequencyspectrum,i.e.theyhavebetterlocalizationoffrequencycomponentsalongthefrequencyaxis,whilethediscontinuously-shapedwavelets(theS^r'swavelet,forexample)havebetterresolutionalongthetimeaxis.Referringtotheoverviewofpropertiesofmanywaveletstypes,theAuthorsdrewaconclusionthattheHaar’swavelet’spropertiesmeetinthebestwaytherequirementsoftheconsideredapplication,regardingboththemetrologicalaspectsasthespeedofreal-timecalculationscarriedoutinprotections.ThebasicHaar’swaveletisdefinedasfollows:f11(0JtJ2)1W(t)={—1(—JtJ1)(7)20(其它)andgeneratesasetofwaveletswithelementsas中(t)=2-m/2中(2-mt—n)m,n=…，-2,-1,0,1,2,…(8)Advantageoftheymnfunctioninproposedapplicationistheirgoodlocalizationasforaninfinitelypreciselocalizationintimeisobtainedenablingarbitraryaccuracy

oflocalizationofthefunctiondiscontinuity(especiallythatofthestep-seeFigures5and6),thefunctionexpansionbeingdefinedregardingtheHaar'swaveletset.TheHaar’sscalingfunctionisgivenbyrelationship:11(0<t<1)(9)"')」0(其它)(9)Presentedrealizationofmeasuringsignalsmulti-leveldecompositionischaracterizedbyhighcalculationefficiency.InresultofapplicationofasimpleHaar’swavelet,decompositionateachlevelislimitedtocalculationoftheaveragevalue(low-passfilter)orofadifference(highpassfilter).Theaveragevalueisaroughrepresentation(approximation)whilethedifferenceisapreciserepresentation(adetail).Fig.8SignalwavelerdecQinpositicntree(WD}DECOMPOSITIONOFMEASURINGSIGNALSANDDAMAGEDLINEDISCRIMINATIONDURINGINTERMITTENTEARTHFAULTSFig.8SignalwavelerdecQinpositicntree(WD}Todiscriminatethelineinwhichtheearthfaultoccurred,theiterativemethodofmeasuringsignalsdecomposition(WD)presentedinsectionIVwasapplied.Thezerocurrentcomponentmeasuredintheshort-circuitedline,701,andhealthyline,I02,havebeenanalysed.Infigures9through14,thesix-leveldecompositionofsignalsobtainedforconsideredB-C-andD-typeintermittentfaultsareshown.ThereportedresultshavebeenobtainedusingthebasicHaar’swavelet,atsamplingfrequencyof10kHz.Infigures,thecharacteristicfeaturesofsignalinvariousfrequencyranges,theiramplitudesandpositiononthetimeaxisareevident.attheinstantscorrespondingtothecommutationphenomenaisespeciallyvisibleatthed1,d2andd3levels.Athigherdecompositionlevels,d4,d5,d6,localizationduringcommutationphenomenabecomeeitherlessvisible(intheundamagedline)ordominating(inthedamagedline).Suchafactcanformabasisforthedamagedlinediscriminationi.e.fordistinctionofthelatterfromtheundamagedone.Occurrenceofevident‘spikes’atthesignal’sdiscontinuityinstantsleadstothesignalaveragevaluemuchlowerthanthepeakvalue.

Atthed4,d5andd6levelsalongwiththehighfrequencycomponents,arunproportionaltotheabsoluteaveragevalue(i),thek-thvalueofwhichcalculatedintheMwidthwindowcanbefoundfromtherelationship:i=N£abs[i(k-n)]；n(10)ispresented.Itisassumedthattheshortedline’sdiscriminationduringtheintermittentearthiscarriedoutbycomparingtheCratiooftheabsoluteinstantaneousvalueandabsoluteaveragevaluetothestart-upvalueoftheCrratio:C=abs(i(k))>C；TOC\o"1-5"\h\z一L(k)r'(11)\o"CurrentDocument"1i-I□LAjAAAAzVAjACjA八八八jAZjA八zm/II_]_L一|触A停X，»g*m”■卜n”»”，MM打d21110；-片-***・A**，PAp，*■食,*■・■**(IjStopd611——--二二二d60讪岫型nW曾冲加叫心虬叫MpgWgk妙ma6：?0Time,ms遍Pig.10.Five-leveldecompositictiofcumentsignal,Undamagedlin^3B-typemreimineutfarlrd6o-i•015十且1oTime,ms440R.ys.11.Five-leveldecompositionofcurrentsignal.Z02；damagedline,C-typeuiterminentfaultTOC\o"1-5"\h\z1y-10.5t1di?444-~!■0j5'(J20+!d3o!+.・・‘*-...・+■■・.».・・.，-1」>0,5r丁二「了1d40-0?5j10.5i：：；：[；；：-二二[T；ij二二JJiUli(15o创神网f邮伸册0声-j'i—m(16o!JJiUli-1】!\o"CurrentDocument"0.25110,25110一・440vlune?msFig.12Five-leveldecompositionofcurrentsignal,Z02：undamagedlineC・typeintermittentfaultRys.L3.Five-leveldecompo^iiioncfcmreatsignal.7o2；damagedline,D-typeluterauTtentfhuhWhentheprotectionmeetsthecondition(11),thebreakerwillopenprovidedthatthezerovoltagecomponent,(OS1=1),provingtheexistenceoftheearthfaultstillremains,andanypulse(OS)switchingofftheadmittancepartofprotection(OS2=0)wasnotsentout.Thealgorithmrepresentingthedescribedideaofdiscriminationofthelinetouchedbyanintermittentfaulttoground(PAC)isshowninFig.15111o0卜/VVV\/\yVVVWW\AA/WVvidl0,ot^-0,51l-rd2of-i-1Td3o：f~^-1XTOC\o"1-5"\h\zwh.-05【」05丁—二、[二(15°・0就d6o.1【!\o"CurrentDocument"°%Time,ms")Rys.14.Five-le\-eldecompositionofcuirentsignal.I02；undamagedline.D-typeintennitreatfaultInFig.16,theblockschemeofanadaptiveearthfaultprotectionbeinganextensionoftheconventionaladmittancetypeprotection(seeFig.2)ispresented.Basicsupplementaryblocksare:WDblockinwhichthemulti-leveldecompositionofneasuringsignalstakesplace,andthePACcomparator(peak-averagecomparator)inwhichthelinediscriminationalgorithmisimplemented(seeFig.15).Rys-.16.AdaptiveuetrrhfaultpioTectioii一block5-ch^meDuetothelogicstructureofprotection,theWDandPACblocksenhancefunctionalityandreliabilityofthefaultseliminationwheretheprotectionsoperatingaccordingtotheclassiccriterionsareunreliable.FINALREMARKSReportedexamplesoftheU0andI0measuringsignalsduringtheintermittentearthfaultsshowthatdetectionofsuchfaultsaswellasidentificationofdamagedlinecanposeproblemstotheconventionalearthfaultprotectingdevices.Thedifficultiesarehigherwhentheinnerpauseduringthefaultexceedstensofmilliseconds.Assuchpausescanoccurinthebalancedmediumvoltagedistributionnetworks,anumberofnon-brokenoffearthfaultsshouldbeexpected.Therefore,newprotectivecriterionseliminatingsuchatroublearetobesearched.Havinganalysedtheexamplesofintermittentfaultsitcanbeeasilyperceivedthatthemultilevelwaveletdecompositionenablestoseparatethesignalfeaturestypicalfortheprotectedlineconditions.Allreportedexampleshaveshownthatthedisturbanceoftheoriginalsignalappearsespeciallyevidentatinitialdecompositionlevels(d1,d2,d3)forthesignalscomingfromboththedamagedl